On 01.08.19 09:48, Michal Hocko wrote: > On Thu 01-08-19 09:39:57, Michal Hocko wrote: >> On Thu 01-08-19 09:31:09, David Hildenbrand wrote: >>> On 01.08.19 09:26, David Hildenbrand wrote: >> [...] >>>> I am not sure about the implications of having >>>> pfn_valid()/pfn_present()/pfn_online() return true but accessing it >>>> results in crashes. (suspend, kdump, whatever other technology touches >>>> online memory) >>> >>> (oneidea: we could of course go ahead and mark the pages PG_offline >>> before unmapping the pfn range to work around these issues) >> >> PG_reserved and an elevated reference count should be enough to drive >> any pfn walker out. Pfn walkers shouldn't touch any page unless they >> know and recognize their type. > > Btw. this shouldn't be much different from DEBUG_PAGE_ALLOC in > principle. The memory is valid, but not mapped to the kernel virtual > space. Nobody should be really touching it anyway. > I guess that could work (I am happy with anything that gets rid of offline_pages()/device_online() here :D ). So for each node, alloc_contig_range() (if I remember correctly, all pages in the range have to be in the same zone), set them PG_reserved (+ maybe something else, we'll have to see). Then, unmap them. The reverse when freeing the memory. Guess this should leave the current user space interface unmodified. I can see that guard pages use a special page type (PageGuard), not sure if something like that is really required. We'll have to see. -- Thanks, David / dhildenb
